The prior art packaging of printed circuit boards containing electronic circuitry to prevent EMI signals from leaving the package or from reaching and adversely affecting highly-susceptible electronic circuitry within the package is both labor intensive to manufacture and service and suffers from several functional limitations. Keeping EMI from leaving an electronics module that contains EMI-emitting components has required soldering certain shielding materials to the printed circuit board and fastening other shielding materials to the soldered shielding material using various screws or other fastening hardware. Keeping EMI from reaching and affecting susceptible electronic circuits in an electronics module, on the other hand, has required placing the printed circuit board fully in a sealed box made of a material that effectively shields most of the EMI signals.
U.S. patent application Ser. No. 07/834,908, entitled "EMI Shield Apparatus and Methods" by W. F. Weber and assigned to "the assignee of the present invention" (the Weber Shield) describes a solderless EMI shield apparatus that overcomes the limitations of prior art devices. Even with the improvements of the Weber Shield, there is a need for an EMI internal shield that effectively separates certain electronic circuits from the rest of the electronic circuitry on a printed circuit board. For example, if certain electronic circuits under the Weber Shield require isolation or shielding from the remaining circuitry, there is no known apparatus or method that provides a solderless, easily removable internal shield. Prior art devices for internal shielding require labor-intensive welding or soldering of multiple shield pieces that may later inhibit repair or replacement of electronic circuitry.
It is an object of the present invention, therefore, to provide an EMI internal shield that may be used with an EMI shield such as the Weber Shield and that effectively separates certain electronic circuits from other electronic circuitry on a printed circuit board to shield the certain electronic circuits from EMI that the other electronic circuitry emits and EMI that may penetrate through the EMI shield, while permitting communication of desired electromagnetic radio frequency and electrical signals with the certain electronic circuits.